Windows Infrared Port Programming (using USPP)

Grant Edwards grante at
Thu Aug 29 20:33:06 CEST 2002

In article <SJtb9.3526$pw.4884179 at>, Grant Edwards wrote:

>> I believe this indicates that I would use COM4 in a program,
>> the OS takes the COM4 data and handles the conversion to
>> Infrared protocol with the IR port being a physical COM2 for
>> interrupt purposes.
> The UART handles the IR part of it.  To Windows, it's just
> another serial port.  The OS doesn't have to know about IR any
> more than it has to know about RS-232 voltage levels and slew
> rates.

I may have oversimplified -- there is usually a configuration
bit in one of the UART registers that tells the UART whether
it's attached to IR LED and phototransistor or to "normal" line
drivers/receivers.  If you've got a dual-interface setup (not
common), there may be a BIOS setting or ioctl() call for
switching from one to the other.

On most laptops I've seen, COM2 (if enabled) is IR-only, COM1
is RS232-only.  All you have to do is check the BIOS to make sure
COM2 isn't disabled in the mobo chipset configuration.

Grant Edwards                   grante             Yow!  I feel like a wet
                                  at               parking meter on Darvon!

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